What is the greatest common factor that could be used to reduce 36/90

For this case, we observe that both the numerator and the denominator of the fraction are multiples of the following numbers:
 2,3,6
 Then we observe that the biggest common factor is 6.
 Taking out common factor we have:
 36/90 = ((6) / (6)) * (6/15) = 6/15
 
 the greatest common factor that could be used to reduce 36/90 is:
 6